Downhill process

The very fact that the A-to-D conversion is a downhill process implies that a chain reaction may take place in the solution, in parallel to the electrode process (Scheme 2.12). After initiation by an electron (or a hole) coming from the electrode, the propagation loop involves the conversion of B into C and the oxidation of the latter by A. When > c, the solution electron transfer is a downhill reaction, whereas for , B < , c, it is an uphill reaction. It may, nevertheless, interfere in the latter case since the entire process is pulled by the B/C reaction. As sketched in Scheme 2.10, the interference of the solution electron transfer is more important for slower B/C conversion. More precisely, the factor governing the interference of the solution electron transfer is the same as in the ECE-DISP problem discussed in Section 2.2.4 (kecPA/ (Fv/ R-T)1/2. Apparently, disconcerting phenomena take place upon interference of the solution electron transfer, such as dips in the current-potential trace when (Figure 2.25a ) and trace crossing... 

Transport across biological membranes is classified according to the thermodynamics of the process. Passive transport is a thermodynamically downhill process the species move toward the equilibrium. The driving force for the passive transport is the potential difference between the two sides of the membrane. Active transport is a thermodynamically uphill process, it is coupled to a chemical reaction and is driven by it. The following transport mechanisms have been recognized ... 

Molecular dynamic simulations are very useful for solvation dynamic studies. In contrast to the difficulties described in applying numerical methods to the problems of vibrational relaxation (Section 13.6) and barrier crossing (Section 14.7), solvation dynamics is a short-time downhill process that takes place (in pure simple solvents) on timescales easily accessible to numerical work. 

FIGURE 13.1 A schematic representation of (i) an activated and (ii) a diffusive energy landscapes and their corresponding trajectories. The diffusive energy landscape is typical for downhill processes that follow protein activation (e.g., in the case of allosteric transition in which local perturbation fundamentally changes the shape of the underlining energy surface). 

Exergonic reactions are "downhill" processes overall in terms of energy, and the product is favored at equilibrium. Reaction (a) is faster than reaction (b) because the activation energy barrier (E, ) is lower for (a) than for (b). 

The second step of the reaction includes the relaxation of the olefin to a planar skeleton and its movement away from the metal (the final Pd-C distance considered is 3.25 A, the same as assumed in Ae first mechanism). This is a downhill process. It is the... 

A spontaneous process is energetically favorable it is a downhill process. Although spontaneous processes are energetically favorable, spontaneity is no guarantee that a process will occur, nor does it indicate how fast a process will occur. Many spontaneous processes do not occur because they are impeded by kinetic barriers. Thus, our calculation of AG only provides us the first step in our quest to understand the rate of processes. Once we have determined AG for a process, we will then need to apply kinetic laws to determine how quickly (if at all) the process will happen ... 

It is a downhill process when the nucleophile is the conjugate base of a weak acid (methanol) and the leaving group is the conjugate base of a strong acid pK is small). Consequently, the reverse reaction is much more difficult. 

We shall call this rate the nucleation rate for the polymer translocation process. Once the barrier in Figure 10.9a is crossed, the translocation process is generally a downhill process. The role of the entropic barrier in controlling the translocation is captured by Equation 10.33. It is in the familiar Arrhenius form or equivalently the Kramers-type form. The nucleation time is the average time taken by the polymer chain to put sufficient number of monomers on the receiver side, after crossing the nucleation barrier, for further progress of the translocation event. We define the nucleation time as the reciprocal of the nucleation rate,... 

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